This invention relates to heat shield arrangements for hot-rolling mills.
Such arrangements are known, e.g. from EP No. 0 010 976, comprising lightweight heat insulating panels disposed around the hot material path through the mill, e.g. including upper and lower panels above and below said path, and possibly also side panels at laterally opposite sides of said path. In that earlier patent, heat shield arrangements are described that provide a relatively restricted vertical spacing between the upper panels and the top surface of the hot material moving along the path through the mill, thereby bringing the radiating hot faces of the panels close to the surfaces of the hot material and achieving a high operational efficiency.
In practice it is found that for wide strip mills--i.e. of about 1.4 meters or greater in width, a distance of about 200 mm between the top surface of the hot metal strip and the radiating bottom face of the upper panels of the heat shield arrangement is able to provide high efficiency operation for a wide strip. If, however, narrower material is passed along the path through the mill, the thermal efficiency falls off.
This problem is felt especially in narrow strip mills which have a reversing roughing stand. It is customary to employ such mills for rolling a large range of widths--thus a mill that can roll material 700 mm wide may frequently be required to roll material as narrow as 200 mm. In the latter case a clearance of 200 mm, such as would be satisfactory for wide strip in a wide strip mill, results in a substantial loss of performance and considerably lower clearances are required to give adequate heat conservation. The problem is increased in such narrow strip mills which employ a multi-stand finishing train: the hot material passes from the roughing stand to the finishing train with a much greater thickness than the strip would have in most wide strip mills, and the finishing train entry speeds are considerably lower. As a result the tail end of the strip is held on the delay table for considerable periods, which can lead to an excessive temperature drop.